1. Field of the Invention
The present invention relates to the communication field and, more particularly, to a repeater and its self-excitation detecting method and system.
2. Description of Related Art
A repeater is an important component of the communication system and has a direct effect on the stability of the whole communication system. With the development of communication industry, the requirements for the repeater become stricter. The repeater, as an amplifying device, may cause a self-excitation if its engineering design is improper. The self-excitation will exert an influence on the repeater and seriously affect the relevant base station, thereby resulting in that the whole communication system fails to work normally, which will affect the quality of communication and may further lead to the paralysis of the whole communication network. Especially, CDMA system is more sensitive to the repeater self-excitation because it is a self-interference system with network coverage of respiration effect.
When the self-excitation occurs in the repeater, it is generally dealt with by the following two methods. In one method, the professional personnel use a testing device to detect the self-excitation by patrol inspection. However, this method involves the cost of manpower and instruments etc, and responds slowly due to the fact that the patrol inspection may not be at the right time. Or the self-excitation is dealt with only when it has an effect on the operation of network, so customers become increasingly unsatisfied with this method. The other method refers to that there should be an enough isolation between the donor antenna and the repeater antenna during engineering design, so as to avoid the generation of self-excitation. Generally an enough distance is kept between the donor antenna and the repeater antenna, or a shielding mesh is disposed between the donor antenna and the repeater antenna, ensuring a proper isolation between the donor antenna and the repeater antenna. However, this method is seldom put into operation because it may be subject to the limitation of geographic location or involve the increase in the cost of engineering design.
FIG. 1 is a structural block diagram of the existing repeater. As shown in FIG. 1, the repeater is mainly composed of a donor antenna 101, a first duplexer 102, an up power amplifier 103, a monitoring unit 104, a first radio-frequency numerically-controlled attenuator 105, an up low-noise amplifier 106, a second duplexer 107, a repeater antenna 108, a down power amplifier 109, a second radio-frequency numerically-controlled attenuator 110, and a down low-noise amplifier 111. The working process is described below in detail.
Working process in the down link is that: the donor antenna 101 receives from the space a downlink signal that may contain some noises, and then the downlink signal enters the first duplexer 102 of the repeater through a radio frequency connection cable. The first duplexer 102 sorts out the signal with the set frequency range by filtering, and sends the signal to the down low-noise amplifier 111 in which the weak signal is amplified. After amplification, the downlink signal, via the second radio-frequency numerically-controlled attenuator 110, is sent to the down power amplifier 109 in which the downlink signal is amplified into the high power downlink signal. Then the downlink signal, via the second duplexer 107, is transmitted to the repeater antenna 108 which in turn emits the downlink signal to the area required to be coverage. The processes of receiving, amplifying and retransmitting the downlink signal to the specified area are thus accomplished.
Working process in the up link is that: the repeater antenna 108 receives from the space the uplink signal that may contain some noises, and then the uplink signal enters the second duplexer 107 of the repeater through the radio frequency connection cable. The second duplexer 107 sorts out the signal with the set frequency range by filtering, and sends the signal to the up low-noise amplifier 106 in which the weak signal is amplified. After amplification, the uplink signal, via the first radio-frequency numerically-controlled attenuator 105, is sent to the up power amplifier 103 in which the uplink signal is amplified into the high power uplink signal. Then the uplink signal, via the first duplexes 102, is transmitted to the donor antenna 101 which in turn emits the uplink signal to the receiving base station. The processes of receiving, amplifying and retransmitting the uplink signal to the specified receiving base station are thus accomplished.
In practice, if there is insufficient isolation between the donor antenna 101 and the repeater antenna 108, the signal emitted by the repeater antenna 108 may be received by the donor antenna 101. Due to the fact that the signal lies within the working frequency range of the repeater, the signal may be amplified again using the process discussed above, generating a positive feedback and continuously circulating in this way, which is the so-called self-excitation. If the self-excitation occurs in the repeater, the signal of positive feedback can have a significant effect on local communication signals, and may burn down the devices in the repeater or even lead to the paralysis of communication system in case of a severe self-excitation.
At present, with the fierce competition in the telecommunication industry, it is urgent to ensure the reliability of communication system as well as the betimes of solving problems. Therefore, it is required to design a method to detect the self-excitation in the repeater in time and remove the defects in the system in real time in case of self-excitation existing in the devices of repeater, so as to solve the problems that the patrol inspection personnel fail to deal with in time.